Semiconductor product with interlocking metal-to-metal bonds and method for manufacturing thereof

ABSTRACT

A structure and method for performing metal-to-metal bonding in an electrical device. For example and without limitation, various aspects of this disclosure provide a structure and method that utilize an interlocking structure configured to enhance metal-to-metal bonding.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

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FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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SEQUENCE LISTING

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MICROFICHE/COPYRIGHT REFERENCE

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BACKGROUND

Present methods for forming electrical connections, for example inintegrated circuits, have shortcomings. For example, though soldering ispopular, solder has a relatively low melting point, which placestemperature limits on subsequent processing steps as well as on thefinished product. Also, solder atoms tend to migrate along copperjoints, thereby changing the electrical and mechanical properties ofsoldered joints as they age. Direct metal-to-metal (e.g.,copper-to-copper (Cu—Cu) bonds, etc.) obviates the need for solder, butcost effective processes for producing such bonds on a large scale haveproven elusive since high temperatures, high pressures, and long dwelltimes complicate, add cost to, and add delay to the assembly process.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an example metal-to-metal bond and bonding method, inaccordance with various aspects of the present disclosure.

FIG. 2 shows an example interlocking metal-to-metal bond and bondingmethod, in accordance with various aspects of the present disclosure.

FIG. 3 shows a perspective view of an example interlocking structure andbonding method, in accordance with various aspects of the presentdisclosure.

FIG. 4 shows a cross-sectional view of an example interlocking structureand bonding method, in accordance with various aspects of the presentdisclosure.

FIG. 5 shows cross-sectional views of an example interlocking structureand bonding method, in accordance with various aspects of the presentdisclosure.

FIG. 6 shows a cross-sectional view of an example interlocking structureand bonding method, in accordance with various aspects of the presentdisclosure.

FIG. 7 shows cross-sectional views of example interlocking structuresand bonding method, in accordance with various aspects of the presentdisclosure.

FIGS. 8A-8E show cross-sectional views of various stages of a method offorming an interconnection structure, in accordance with various aspectsof the present disclosure.

FIGS. 9A-9C show cross-sectional views of various stages of a method offorming an interconnection structure, in accordance with various aspectsof the present disclosure.

SUMMARY

Various aspects of this disclosure provide a structure and method forperforming metal-to-metal bonding in an electrical device. For exampleand without limitation, various aspects of this disclosure provide astructure and method that utilize an interlocking structure configuredto enhance metal-to-metal bonding.

DETAILED DESCRIPTION OF VARIOUS ASPECTS OF THE DISCLOSURE

The following discussion presents various aspects of the presentdisclosure by providing examples thereof. Such examples arenon-limiting, and thus the scope of various aspects of the presentdisclosure should not necessarily be limited by any particularcharacteristics of the provided examples. In the following discussion,the phrases “for example,” “e.g.,” and “exemplary” are non-limiting andare generally synonymous with “by way of example and not limitation,”“for example and not limitation,” and the like.

As utilized herein, “and/or” means any one or more of the items in thelist joined by “and/or”. As an example, “x and/or y” means any elementof the three-element set {(x), (y), (x, y)}. In other words, “x and/ory” means “one or both of x and y.” As another example, “x, y, and/or z”means any element of the seven-element set {(x), (y), (z), (x, y), (x,z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means “one ormore of x, y, and z.”

The terminology used herein is for the purpose of describing particularexamples only and is not intended to be limiting of the disclosure. Asused herein, the singular forms are intended to include the plural formsas well, unless the context clearly indicates otherwise. It will befurther understood that the terms “comprises,” “includes,” “comprising,”“including,” “has,” “have,” “having,” and the like when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, for example, a first element, afirst component or a first section discussed below could be termed asecond element, a second component or a second section without departingfrom the teachings of the present disclosure. Similarly, various spatialterms, such as “upper,” “lower,” “side,” and the like, may be used indistinguishing one element from another element in a relative manner. Itshould be understood, however, that components may be oriented indifferent manners, for example a semiconductor device may be turnedsideways so that its “top” surface is facing horizontally and its “side”surface is facing vertically, without departing from the teachings ofthe present disclosure. Additionally, the term “on” will be utilized inthe document to mean both “on” and “directly on” (e.g., with nointervening layer).

In the drawings, various dimensions (e.g., layer thickness, width, etc.)may be exaggerated for illustrative clarity. Additionally, likereference numbers are utilized to refer to like elements through thediscussions of various examples.

The discussion herein will generally provide examples in the context ofcopper-to-copper bonding. It should be understood, however, that thescope of this disclosure is not limited thereto. For example, thevarious aspects of this disclosure also apply to other metal-to-metalbonds (e.g., Au-to-Au bonds, Ag-to-Ag bonds, etc.). Also for example,various alloys may also be utilized (e.g., copper alloys, silver alloys,gold alloys, etc.). Note that metals may also comprise various levels ofimpurities. For example, a copper pillar may essentially be formed of100% copper, but may also have a certain percentage of impurities.

In an example implementation provided herein, a method of manufacturinga semiconductor device comprises: providing a first substrate comprisinga first copper contact structure, the first copper contact structurecomprising a dome-shaped end; providing a second substrate comprising asecond copper contact structure, the second copper contact structurecomprising a dish-shaped end that has a dish depth; mating thedome-shaped end and the dish-shaped end, such that the dome-shaped endcontacts the dish-shaped end at multiple points around a perimeter ofthe dome-shaped end and only at a distance into the dish-shaped cavitybetween 5% and 95% of the dish depth; and pressing the mated dome-shapedend and dish-shaped end together to form a copper-to-copper bond. Alsoprovided is an electronic device produced in accordance with suchexample method.

In an example implementation provided herein, a method of manufacturinga semiconductor device comprises: providing a first substrate comprisinga first metal contact structure of a metal, the first metal contactstructure comprising a convex-shaped end that comprises: a first convexportion having a first convex radius of curvature; and a second convexportion having a second convex radius of curvature; providing a secondsubstrate comprising a second metal contact structure of the metal, thesecond metal contact structure comprising a concave-shaped end thatcomprises a first concave portion having a first concave radius ofcurvature, wherein: the first concave radius of curvature is less thanthe first convex radius of curvature; and the first concave radius ofcurvature is greater than the second convex radius of curvature; matingthe convex-shaped end and the concave-shaped end, such that the secondconvex portion contacts the concave-shaped end at multiple points arounda perimeter of the concave-shaped end and the first convex portion doesnot contact the concave shaped end; and pressing the mated convex-shapedend and concave-shaped end together to form a metal-to-metal bond of themetal. Also provided is an electronic device produced in accordance withsuch example method.

In an example implementation provided herein, a method of manufacturinga semiconductor device comprises: providing a first substrate comprisinga first metal contact structure of a metal, the first metal contactstructure comprising a convex-shaped end; providing a second substratecomprising a second metal contact structure of the metal, the secondmetal contact structure comprising a concave-shaped end that comprises acenter point, an edge, and a center-to-edge distance along a surface ofthe concave-shaped end between the center point and the edge; mating theconvex-shaped end and the concave-shaped end, such that theconvex-shaped end contacts the concave-shaped end at multiple pointsaround a perimeter of the convex-shaped end and only at a distance fromthe center point greater than 10% and 90% of the center-to-edgedistance; and pressing the mated convex-shaped end and concave-shapedend together to form a metal-to-metal bond of the metal. Also providedis an electronic device produced in accordance with such example method.

FIG. 1 shows an example metal-to-metal bonding process. As shown atlabel 100, two substrates 110, 120 have copper contact (orinterconnection) structures 112, 122, which may also be referred toherein as contacts, which are to be joined. The substrates 110 and 120may comprise any of a variety of characteristics. For example, one orboth of the substrates 110 and 120 may comprise a semiconductor die(e.g., in wafer form, in panel form, in individual diced form, etc.).Also for example, one or both of the substrates 110 and 120 may comprisean interposer (e.g., formed on a carrier (e.g., a glass carrier, a metalcarrier, a silicon carrier, etc.) which is removed after the formation,etc.). Additionally for example, one or both of the substrates 110 and120 may comprise a laminate substrate (e.g., a packaging substrate, amotherboard, etc.). Accordingly, the scope of this disclosure should notbe limited by characteristics of any particular type of substrate.

The copper contacts 112 and 122 are presented as drawn for illustrativepurposes, but may for example comprise characteristics of any of avariety of different types of interconnection structures. For example,one or both of such contacts 112 and 122 may comprise a metal pillar orpost (e.g., with generally vertical side surfaces). Also for example,one or both of such contacts 112 and 122 may comprise a metal pad ortrace. Additionally for example, one or both of such contacts 112 and122 may comprise a longitudinal length (or height) that is greater thana lateral width; and/or one or both of such contacts 112 and 122 maycomprise a lateral width that is greater than a longitudinal length (orheight). Note that in various example implementations, the first contact112 and the second contact 122 may be formed of a same metal (e.g.,copper, etc.), but this need not be the case. In another exampleimplementation, an intervening metal may be formed between the firstcontact 112 and the second contact 122.

Though many of the examples presented herein show such contacts 112 and122 in a cylindrical shape, any of a variety of shapes may be utilized.For example, one or both of the contacts 112 and 122 may have arectangular cross-section (e.g., cross-section cut perpendicular to avertical axis, cross-section cut perpendicular to a horizontal axis,etc.). Also for example, one or both of the contacts 112 and 122 mayhave a generally polygonal (e.g., N-sided, where N is an integer)cross-section (e.g., cross-section cut perpendicular to a vertical axis,cross-section cut perpendicular to a horizontal axis, etc.).Additionally for example, one or both of the contacts 112 and 122 mayhave a circular or elliptical cross-section (e.g., cross-section cutperpendicular to a vertical axis, cross-section cut perpendicular to ahorizontal axis, etc.).

Further, many of the examples presented herein show the first contact112 (e.g., a pillar or post, long pillar or post, etc.) beinglongitudinally vertically in the figures) longer than the second contact122 (e.g., a pad or pedestal, short pillar or post, etc.). It should beunderstood that such relative lengths are merely illustrative andnon-limiting. For example, the first contact 112 and the second contact122 may be of equal length, the second contact 122 may be longer thanthe first contact 112, etc. Also, the first contact 112 and the secondcontact 122 are generally illustrated herein as having a same or similaraxial width (e.g., horizontal dimension in the figures). It should beunderstood that such relative widths are merely illustrative andnon-limiting. For example, the first contact 112 may be narrower thanthe second contact 122, the second contact 122 may be narrower than thefirst contact 112, etc. Also for example, the first contact 112 may havea width (e.g., a largest width at a widest portion thereof) that is lessthan the width (e.g., largest width at a widest portion thereof) of thesecond contact 122, the second contact 122 may have a width (e.g.,largest width) that is less than the width (e.g., largest width) of thefirst contact 112, etc.

Though only one mating pair of interconnection structures isillustrated, it should be understood that many identical structures maybe formed on the substrates. For example, the illustrated contacts 112and 122 may be one of tens or hundreds of same or similar structuresutilized to electrically and/or mechanically couple the substrates 110and 120. For example, such contacts may be spaced relatively closelytogether (e.g., at a pitch (or center-to-center spacing) of 50 micronsor less, 30 microns or less, etc.).

In various implementations, the first contact 112 and/or the secondcontact 122 may be formed in any of a variety of manners. For example, ametal pad or trace may be formed on a silicon substrate and exposedthrough a dielectric (or passivation) layer. Note that such pad or tracemay be part of a multi-layer signal distribution structure. One or moreseed layers and/or under bump metal (UBM) layers may be deposited (e.g.,sputtered, plated, etc.) on the pad or trace, and the contact(s) may beformed on such seed and/or layer(s), for example through openings in adielectric template, which may then be removed. Though in variousimplementations, a solder cap may be formed on the contact, inaccordance with various aspects of this disclosure, the formed contacts,or the tips thereof, may be left bare (e.g., without solder).

Accordingly, the scope of this disclosure should not be limited byparticular characteristics of the interconnection contacts (e.g., thefirst contact 112 and/or the second contact 122, etc.) or by anyparticular manner of making such contacts.

At label 150, the substrates 110, 120 are brought together (or mated) tobring the copper contact 112 in contact with the copper contact 122. Toform a Cu-Cu bond at the interface between the copper contacts 112 and122, high pressure and high heat are generally applied for a substantialdwell time. If the two mated surfaces of the copper contacts 112 and 122are clean (e.g., perfectly clean, etc.), then random atomic motion willeventually cause atoms to traverse the interface between the twosurfaces, thus blurring the interface, and over time the interface maydisappear entirely.

However, this is a slow process because the atomic motion is generallyrandom (e.g., mostly or completely random). Example pressures may forexample be greater than 200 MegaPascals (MPa), example temperatures mayfor example be greater than 300 C, and example dwell times may forexample be on the order of an hour to several hours.

Turning now to FIG. 2, such figure shows an example interlockingmetal-to-metal bond and bonding method, in accordance with variousaspects of the present disclosure. The example structures and methods ofFIG. 2, or any portion thereof, may share any or all characteristicswith other analogous structures or methods discussed herein (e.g., withregard to FIGS. 1 and 3-9),

As shown at label 200, two substrates 210 and 220 have copper contacts212 and 222 that are to be joined. As discussed herein (e.g., withregard to FIG. 1, etc.), the substrates 210 and 220 may comprise any ofa variety of characteristics and/or may be formed in any of a variety ofmanners. Also as discussed herein (e.g., with regard to FIG. 1, etc.),the copper contacts 212 and 222 may comprise any of a variety ofcharacteristics and/or may be formed in any of a variety of manners.

As will be discussed in detail herein, the first copper contact 212comprises a convex-shaped (e.g., dome-shaped, etc.) end, and the secondcopper contact 222 comprises a concave-shaped (e.g., dish-shaped, etc.)end.

The first copper contact 212 may, for example, be formed utilizing ametal plating operation. The shape of the end of the first coppercontact 212 (e.g., the end that is to contact a corresponding end of thesecond copper contact 222) may be formed to have a convex shape. Such ashape may, for example, be obtained by adjusting various plating processparameters. For example, in an example implementation, a convex-shapedend may be obtained by increasing the concentration of a levelerutilized in the plating process. For example, a convex end (or dome)height of greater than 10% or 15% of the overall height of the contactmay be obtained by doubling the concentration of leveler utilized toobtain a generally flat end.

The second copper contact 222 may, for example, be formed utilizing ametal plating operation. The shape of the end of the second coppercontact 222 (e.g., the end that is to contact a corresponding end of thefirst copper contact 212) may be formed to have a concave shape. Such ashape may, for example, be obtained by adjusting plating processparameters. For example, in an example implementation, a concave-shapedend may be obtained by decreasing the concentration of a levelerutilized in the plating process. For example, a concave end (or dish)depth of greater than 10% or 15% of the overall height of the contactmay be obtained by halving the concentration of leveler utilized toobtain a generally flat end.

In an example implementation, the degree of convexity and/or concavityat various points on the ends of the contacts may be tuned by adjustingthe concentration of the leveler in a single plating process and/or byadjusting the concentration of the leveler in a plurality of sequentialplating processes. Note that in an example implementation that includesa plurality of sequential plating processes, each plating process neednot cover the exact same area, thus providing a large degree offlexibility in shaping the ends of the contacts.

At label 250, as at label 150 of FIG. 1, the substrates 210, 220 arebrought together (or mated) to bring the copper contact 212 in contactwith the copper contact 222. To form a Cu—Cu bond at the interfacebetween the copper contacts 212 and 222, pressure and heat may beapplied for a dwell time. If the two mated surfaces of the coppercontacts 212 and 222 are clean (e.g., perfectly clean, etc.), thenrandom atomic motion will eventually cause atoms to traverse theinterface between the two surfaces, thus blurring the interface, andover time the interface may disappear entirely. However, if the matingsurfaces of the copper contacts 212 and 222 are exactly matched, thismay still be a slow process, generally as with the example method ofFIG. 1, because the atomic motion is generally random (e.g., mostly orcompletely random). Thus, in accordance with various aspects of thisdisclosure, as discussed herein, the mating surfaces may beintentionally mismatched to enhance the metal-to-metal bonding.

In accordance with various aspects of this disclosure, an underfill maybe formed between the substrates 210 and 220. For example, after theattachment between the copper contacts 212 and 222, an underfill may beformed between the substrates 210 and 220 and/or surrounding the coppercontacts 212 and 222 (e.g., by capillary underfilling, moldedunderfilling, etc.). In another example, before the attachment betweenthe copper contacts 212 and 222, pre-applied underfill (e.g., with anon-conductive paste (NCP), etc.) may be formed on one or more of thesubstrates 210 and 220.

Such underfill formation may, for example, be performed withoutcontaminating the mating ends of the copper contacts 212 and 222 priorto their mating.

Turning to FIG. 3, such Figure shows a perspective view 300 of anexample interlocking structure and bonding method, in accordance withvarious aspects of the present disclosure. The example structures andmethods of FIG. 3, or any portion thereof, may share any or allcharacteristics with other analogous structures or methods discussedherein (e.g., with regard to FIGS. 2 and 4-9).

As discussed herein, the ends of the interconnection structures may beformed to imperfectly mate. FIG. 4 shows a cross-sectional view of anexample interlocking structure and method, in accordance with variousaspects of the present disclosure. The example structures and methods ofFIG. 4, or any portion thereof, may share any or all characteristicswith other analogous structures or methods discussed herein (e.g., withregard to FIGS. 1-3 and 5-9).

The first (or top) copper contact 412 comprises a convex surface 413,and the second (or bottom) copper contact 422 comprises a concavesurface 423 that faces the convex surface 413. The illustration 400 is across-sectional view taken along a longitudinal axis running throughboth of the first copper contact 412 and the second copper contact 422when such contacts are aligned along the longitudinal axis. In thecross-sectional illustration 400, the convex surface 413 is showncontacting the concave surface 423 at a first contact point 432 and at asecond contact point 434. In three dimensions, as will be discussedherein, such contact may extend around the convex surface 413 (e.g.,forming a circle, etc.).

The concave surface 423 comprises a depth 495 (e.g., a largest depth)between the top peripheral edge of the concave surface 423 and a bottompoint (e.g., a center point on the concave surface 423, etc.) of theconcavity. The first contact point 432 and the second contact point 434are shown approximately vertically half way 497 between the topperipheral edge and the bottom point. In various exampleimplementations, the contact points 432 and 434 may be locatedvertically from 25% to 75% of the depth 495 into the concave region(e.g., the dish-shaped region, etc.) from the vertical level of the topperipheral edge. In various other example implementations, the contactpoints 432 and 434 may be located vertically from 10% to 90% of thedepth 495 into the concave cavity from the vertical level of the topperipheral edge, or from 5% to 95% of the depth 495 into the concaveregion from the vertical level of the top peripheral edge; or from 0% to95% of the depth 495 into the concave region from the vertical level ofthe top peripheral edge.

The first contact point 432 and the second contact point 434 may also,for example, be located between 25% and 75% of the distance along theconcave surface 423 from the bottom (or center) point to the topperipheral edge. In another example implementation, the first contactpoint 432 and the second contact point 434 may, for example, be locatedbetween 10% and 90% of the distance along the concave surface 423 fromthe bottom point to the top peripheral edge, or from 5% and 95% of thedistance along the concave surface 423 from the bottom point to the topperipheral edge, or greater than 5% or 10% of the distance along theconcave surface 423 from the bottom point to the top peripheral edge(which may, for example, extend all of the way to the top peripheraledge).

As shown in FIG. 4, a total force F_(T) may be applied to press thefirst copper contact 412 and the second copper contact 422 together.Since at the points of contact 432 and 434, the convex surface 413 andthe concave surface 423 contact each other at an angle that is notorthogonal to the direction of the force F_(T), there is a compressionforce F_(C) component of the force F_(T), which operates to press theconvex surface 413 and the concave surface 423 directly together (e.g.,acting orthogonally to the interface at the points of contact 432 and434). Such a force F_(C) may also be referred to herein as a normalforce. There is also a shear force F_(S) component of the force F_(T),which operates tangentially along the interface between the convexsurface 413 and the concave surface 423 at the points of contact 432 and434.

The combination of the compression force F_(C) and the shear force F_(S)operates on the metal (e.g., the copper, etc.) of the first coppercontact 412 and the second copper contact 422 to cause plasticdeformation. Such plastic deformation may, in turn, increase the degreeof atomic diffusion between the convex surface 413 and the concavesurface 423. Such increased degree of diffusion, in turn, may result inan overall decrease in the amount of pressure, temperature, and/or dwelltime needed to create an effective copper-to-copper bond between thefirst copper contact 412 and the second copper contact 422.

Depending on the amount of deformation of the convex surface 413 and theconcave surface 423, after the metal-to-metal (e.g., copper-to-copper,etc.) bonding has completed, there may be gaps between respectiveportions of the convex surface 413 and the concave surface 423. Notethat this need not necessarily be the case. For example, during thebonding process, enough deformation of the convex surface 413 and/or theconcave surface 423 may occur to eliminate some or all of the gapsbetween the convex surface 413 and the concave surface 423.

FIG. 5 shows cross-sectional views of an example interlocking structure,in accordance with various aspects of the present disclosure. Theexample structures and methods of FIG. 5, or any portion thereof, mayshare any or all characteristics with other analogous structures ormethods discussed herein (e.g., with regard to FIGS. 1-4 and 6-9). Thetop half of FIG. 5 is for example a cross-sectional view cut along thelongitudinal axis e.g., up/down in the example illustrations herein),and the bottom half of FIG. 5 is for example a top-down view of a regionproximate the metal-to-metal bonds.

As mentioned herein, even after the metal-to-metal bonding process,there may be gaps between various respective portions of the convexsurface 513 and the concave surface 523. The example illustration 500provides illustrative examples of such gaps. The size of such gaps may,for example, be exaggerated for illustrative clarity.

The example 500 comprises a middle region 562 corresponding to plasticdeformation of the convex surface 513 and/or the concave surface 523 andmetal-to-metal bonding between the first copper contact 512 and thesecond copper contact 522. The middle region 562, for example, comprisesthe region 551 and region 553, as shown in the upper cross-sectionalview. In an example implementation, the middle region 562 forms a ringaround a middle of the convex surface 513 and within the concave surface523. Also for example, there is a gap in the center region 563 of height(e.g., largest height) D between the convex surface 513 (e.g., a tip orcenter thereof) and the bottom (or center) of the concave surface 523.Additionally for example, there is a gap in the peripheral region 561 ofheight (e.g., largest height) P between the convex surface 513 (e.g., aperipheral edge thereof) and the peripheral edge of the concave surface523.

Though as explained herein, the deformation of the convex surface 513and/or concave surface 523 may be enough to eliminate gaps between suchsurfaces, this need not be the case. For example, the convex surface 513and the concave surface 523 may contact each other and be metal-to-metalbonded to each other in the center region 563 and/or in the peripheralregion 561. Such bonds, if they exist, may for example be weaker (orless complete) than the bond in the bonding region 562 but need not be.For example, in an example implementation, interface lines in the centerregion 563 and/or in the peripheral region 561 between the convexsurface 513 and the concave surface 523 may be more apparent (e.g., morevisible, etc.) after the bonding process than interface lines in themiddle region 562.

Though the example 500 of FIG. 5 is generally illustrated withsymmetrical characteristics, such symmetry is not required. For example,the first contact 512 and/or the second contact 522 may be asymmetric.Such asymmetry, in turn, may lead to asymmetry in the region in Whichthe first contact 512 and the second contact 522 are bonded. Forexample, referring to the bonding region 562 of FIG. 5, such bondingregion 562 may be off-center (or shifted) with regard to the centers ofthe first contact 512 and/or the second contact 522 (e.g., at least 5%or 10% of the contact width, at least a percentage greater than themanufacturing tolerance, etc.). Also for example, one side of thebonding region 562 may be thinner than another side (e.g., the region551 may be shorter than the region 553 or vice versa), for example atleast 5% or 10% of either region width, at least a percentage greaterthan the manufacturing tolerance, etc. Additionally for example, oneside of the bonding region 562 may be positioned differently relative tothe center than another side (e.g., the region 551 may be shiftedrelative to the center while the region 553 is not or is shifted by adifferent amount). Further for example, gap P shown at the left side ofFIG. 5 may be different from an analogous gap at the right side of FIG.5 (e.g., at least 5% or 10% of the gap P width, to a percentage greaterthan the manufacturing tolerance, etc.).

The shapes of various example convex and concave surfaces may also bedescribed in terms of one or more radii of curvature. A non-limitingexample of such characterization is provided at FIG. 6, which shows across-sectional view of an example interlocking structure and bondingmethod, in accordance with various aspects of the present disclosure.The example structures and methods of FIG. 6, or any portion thereof,may share any or all characteristics with other analogous structures ormethods discussed herein (e.g., with regard to FIGS. 1-5 and 7-9).

In the example illustration 600, the first metal contact 612 comprises aconvex surface 613. A portion of the convex surface 613 in a centralregion 655 may, for example, have a radius of curvature of R2. Also forexample, a portion of the convex surface 613 in middle regions 651 and653 may have a radius of curvature of R3. Additionally for example, aportion of the convex surface 613 in peripheral regions 657 and 659 mayhave a radius of curvature of R4.

Also in the example illustration 600, the second metal contact 622comprises a concave surface 623 that has a radius of curvature of R1. Itshould be noted that the concave surface 623 is presented as having asingle radius of curvature, but such characterization is utilized forillustrative clarity. For example, a plurality of portions of theconcave surface 623 may each comprise a different respective radius ofcurvature. In the example illustration 600, R2>R1 and R3<R1.Additionally, R3<R4<R1. In another example implementation R4=R3.

Note that during the bonding process, due to deformation of the convexsurface 613 and/or the concave surface 623, the radius of curvature willgenerally become the same in the regions in which the metal-to-metalbonding occurs. In a first example implementation, in whichmetal-to-metal bonding only occurs in the middle region 662 (e.g.,including the cross-section regions 651 and 653), a gap remains betweenthe convex surface 613 and the concave surface 623 in the center region663 and in the peripheral region 661. In such an example implementation,due to deformation, the radius of curvature of the convex surface 613and the concave surface 623 will become generally the same in the middleregion 662, R2 will remain greater than R1, and R4 will remain less thanR1.

In an example implementation in which metal-to-metal bonding ultimatelyoccurs in the center region 663 as well as the middle region 662, forexample due to deformation, the radius of curvature of the convexsurface 613 and the concave surface 623 will become generally the samein the center region 663 as well as the middle region 662. In an exampleimplementation in which metal-to-metal bonding ultimately occurs in theperipheral region 661 as well as the middle region 662 (e.g., inaddition to or instead of in the center region 663), for example due todeformation, the radius of curvature of the convex surface 613 and theconcave surface 623 will become genera same in the peripheral region 661as well as the middle region 662.

As discussed herein (e.g., with regard to FIG. 5), though the example600 of FIG. 6 is generally illustrated with a symmetricalcharacteristics, such symmetry is not required. For example, the firstcontact 612 and/or the second contact 622 may be asymmetric. Suchasymmetry, in turn, may lead to asymmetry in the region in which thefirst contact 612 and the second contact 622 are bonded. For example,referring to the bonding region 662 of FIG. 6, such bonding region 662may be off-center (or shifted) with regard to the centers of the firstcontact 612 and/or the second contact 622 (e.g., at least 5% or 10% ofthe contact width, at least a percentage greater than the manufacturingtolerance, etc.). Also for example, one side of the bonding region 662may be thinner than another side (e.g., the region 651 may be shorterthan the region 653 or vice versa), for example at least 5% or 10% ofeither region width, at least a percentage greater than themanufacturing tolerance, etc. Additionally for example, one side of thebonding region 662 may be positioned differently relative to the centerthan another side (e.g., the region 651 may be shifted relative to thecenter while the region 653 is not or is shifted by a different amount).Further for example, the R3 (and/or R4) shown at the left side of FIG. 6may be different from the R3 (and/or R4) shown at the right side of FIG.6 (e.g., at least 5% or 10% of R3 (and/or R4), to a percentage greaterthan the manufacturing tolerance, etc.).

As discussed herein, the metal contacts may be cylindrical, rectangular,generally polygonal, etc. In various example implementations, there neednot be a continuous bonding line or region between the convex surfaceand the concave surface, but in other example implementations there maybe a continuous bonding line or region. FIG. 7 shows cross-sectionalviews of example interlocking structures, in accordance with variousaspects of the present disclosure. In such examples, the metal-to-metalbonding regions are distinct, rather than continuous.

For example, in the example illustration at label 700 of FIG. 7, acontact with a square cross-section may deform and bond at four cornerregions 771, 772, 773, and 774. Also example, in the exampleillustration at label 750 of FIG. 7, a contact with an octagonalcross-section may deform and bond at eight corner regions 781-788. Notethat, as discussed herein, due to deformation of the contacts during thebonding process, even in scenarios in which the initial contact betweenthe first and second metal contacts occurs only at distinct points, asthe convex and/or concave surfaces deform, such contact may spread tocreate continuously coupled regions of bonding, and even spread tocreate a comprehensive region of bonding over the entire convex and/orconcave surface.

As mentioned herein, though only one mating pair of interconnectionstructures is generally illustrated and discussed in the examples, itshould be understood that many identical structures may be formed on thesubstrates. For example, the illustrated contacts may be one of tens orhundreds of same or similar structures utilized to electrically and/ormechanically couple the substrates. For example, such contacts may bearranged in an array, a solid matrix, a square or rectangulararrangement, in a line, in parallel lines, etc. It should be understoodthat although all of the contacts may be similar to the contactsdiscussed herein, all of the contacts need not be the same. For example,in an example implementation of an electronic component with a pluralityof the contacts, a first portion of the contacts may be different from asecond portion of the contacts. Also for example, a first portion of thecontacts may be as discussed herein, and a second portion may havesubstantially flat ends. Additionally for example, a first portion ofthe contacts may be asymmetric, and a second portion may be symmetric.Further for example, a first portion of the contacts may have a firstheight, width, or pitch, and a second portion of the contacts may have asecond height, width, or pitch, different from the first height, width,or pitch.

As mentioned herein, the substrate may be in various forms, includingwafer form. Thus, the scope of this disclosure includes wafer levelbumping (e.g., copper pillar wafer level bumping). Examples of a bumpingprocess (e.g., a wafer level bumping process, etc.) are provided inFIGS. 8 and 9.

FIGS. 8A-8E show cross-sectional views of various stages of a method offorming an interconnection structure, in accordance with various aspectsof the present disclosure. The example structures and/or methods shownin FIGS. 8A-8E, or any portion thereof, may share any or allcharacteristics with other analogous structures and/or methods shownherein (e.g., with regard to FIGS. 1-7 and 9). Though the formation ofonly one wafer level bump is illustrated, it should be understood thatsuch formation may be replicated hundreds or thousands of times on asingle wafer. Also note that the scope of this disclosure is not limitedto wafer level operations. For example, any or all of the operationsdiscloses here may be performed on individual die, panels of die, wafersof die.

At FIG. 8A, a substrate 810 comprising a pad 811 (e.g., an I/O pad, abond pad, etc.) is presented (e.g., received, fabricated, etc.). Notethat any number of pads may be present, but only one is shown here forillustrative clarity. The substrate 810 may, for example, comprise asemiconductor die (e.g., a silicon semiconductor die, an active side ofa semiconductor die, a back-side of a semiconductor die with anelectrical connection to the front-side, etc.).

A bond pad 811 may, for example, be formed to cover a top portion of thesubstrate 810 at contact locations. The pad 811 may, for example,comprise any of a variety of conductive materials (e.g., copper,aluminum, silver, gold, nickel, alloys thereof, etc.).

A dielectric layer 812 (which may also be referred to as a passivationlayer) is formed on the substrate 810, for example to cover a top sideof the substrate 810. The dielectric layer 812 may, for example, coverside surfaces of the bond pad 811 and/or an outer perimeter of the topsurface of the bond pad 811. The dielectric layer 812 may comprise anyof a variety of types of materials, for example inorganic materials(e.g., a nitride (Si₃N₄), an oxide (SiO₂), SiON, etc.) and/or organicmaterials (e.g., polyimide (PI), benzo cyclo butane (BCB), poly benzoxazole (PBO), bismaleimide triazine (BT), a phenolic resin, epoxy,etc.), but the scope of the present disclosure is not limited thereto.The dielectric layer 812 may, for example, be formed by any of a varietyof processes (e.g., spin coating, printing, spray coating, sintering,thermal oxidation, Physical Vapor Deposition (PVD), Chemical VaporDeposition (CVD), atomic layer deposition (ALD), etc.). The dielectriclayer 812 may, for example, comprise an aperture through which at leasta portion of the pad 811 is exposed.

A UBM seed layer 813 may be formed over the dielectric layer 812 and/orover the portion of the pad 811 that is exposed through the aperture inthe dielectric layer 812. The UBM seed layer 813 may, for example,comprise any of a variety of conductive materials (e.g., copper, gold,silver, metal, etc.). The UBM seed layer 813 may be formed in any of avariety of manners (e.g., sputtering, electroless plating, CVD, PVD,ALD, etc.).

As shown in FIG. 8B, a mask 821 (or template) is formed and/or patternedover the UBM seed layer 813 to define a region in which a UBM and/orinterconnection structure (e.g., metal pillar, etc.) is to be formed.For example, the mask 821 may comprise a photoresist (PR) material orother material, which may be patterned to cover regions other than theregion on which a UBM and/or interconnection structure is to be formed.

As shown in FIG. 8C, the UBM 831 is formed on the UBM seed layer 813exposed through the mask 821. The UBM 831 may comprise any of a varietyof materials (e.g., titanium, chromium, aluminum, titanium/tungsten,titanium/nickel, copper, alloys thereof, etc.). The UBM 831 may beformed on the UBM seed layer 813 in any of a variety of manners (e.g.,electroplating, electroless plating, sputtering, CVD, PVD, atomic layerdeposition (ALD), etc.).

As also shown in FIG. 8C, the interconnection structure 832 is formed onthe UBM 831. The interconnection structure 832 may comprise any of avariety of characteristics. For example, the interconnection structure832 may share any or all characteristics with any or all of theinterconnections structures (e.g., the contacts 212, 222, 312, 322, 412,422, 512, 522, 612, 622, etc.) discussed herein. The interconnectionstructure 832 may, for example, comprise copper (e.g., pure copper,copper with some impurities, etc.), a copper alloy, nickel, etc.).

As discussed herein, the interconnection structure 832 may be formed tohave a convex-shaped (or dome-shaped) end, for example by adjustingleveler concentration. For example, a convex end (or dome) height ofgreater than 10% or 15% of the overall height of the interconnectionstructure 832 may be obtained by doubling the concentration of levelerutilized to obtain a generally flat end.

As shown at FIG. 8D (e.g., as compared to FIG. 8C), the mask 821 (e.g.,photoresist, etc.) is stripped. The mask 821 may be removed in any of avariety of manners (e.g., chemical stripping, aching, etc.). As shown atFIG. 8E (e.g., as compared to FIG. 8D), the UBM seed layer 813 (e.g., atleast the portion that is not covered by the interconnection structure832) is removed (e.g., chemically etched, etc.). Note that during theetching of the seed layer 813, a lateral edge portion of at least theUBM seed layer 813 may, for example, be etched. Such etching may, forexample, result in an undercut beneath the interconnection structure 832and/or UBM 831.

As discussed herein, an interconnection structure may be formed with aconcave-shaped (or dish-shaped) end instead of with a convex-shaped (ordome-shaped) end. An example of such formation is shown in FIGS. 9A-9C.

FIGS. 9A-9C show cross-sectional views of various stages of a method offorming an interconnection structure, in accordance with various aspectsof the present disclosure. The method shown in FIG. 9 may, for example,share any or all characteristics with the method shown in FIG. 8. Thus,this discussion will focus generally on the differences. The examplestructures and/or methods shown in FIGS. 9A-9C, or any portion thereof,may share any or all characteristics with other analogous structuresand/or methods shown herein (e.g., with regard to FIGS. 1-8). Though theformation of only one wafer level bump is illustrated, it should beunderstood that such _formation may be replicated hundreds or thousandsof times on a single wafer. Also note that the scope of this disclosureis not limited to wafer level operations. For example, any or all of theoperations discloses here may be performed on individual die, panels ofdie, wafers of die, etc.

As shown in FIG. 9A, as with FIG. 8C, the UBM 831 is formed on the UBMseed layer 813 exposed through the mask 821. The UBM 831 may compriseany of a variety of materials (e.g., titanium, chromium, aluminum,titanium/tungsten, titanium/nickel, copper, alloys thereof, etc.). TheUBM 831 may be formed on the UBM seed layer 813 in any of a variety ofmanners (e.g., electroplating, electroless plating, sputtering, CVD,PVD, atomic layer deposition (ALD), etc.).

As also shown in FIG. 9A, as with the interconnection structure 832 ofFIG. 8C, the interconnection structure 832 is formed on the UBM 831. Theinterconnection structure 832 may comprise any of a variety ofcharacteristics. For example, the interconnection structure 832 mayshare any or all characteristics with any or all of the interconnectionsstructures (e.g., the contacts 212, 222, 312, 322, 412, 422, 512, 522,612, 622, etc.) discussed herein. The interconnection structure 832 may,for example, comprise copper (e.g., pure copper, copper with sonicimpurities, etc.), a copper alloy, nickel, etc.).

As discussed herein, the interconnection structure 932 (as opposed tothe example interconnection structure 832 of FIG. 8) may be formed tohave a concave-shaped (or dish-shaped) end, for example by adjustingleveler concentration. For example, in an example implementation, aconcave-shaped end may be obtained by decreasing the concentration of aleveler utilized in the plating process. For example, a concave end (ordish)) depth of greater than 10% or 15% of the overall height of theinterconnection structure 932 may be obtained by halving theconcentration of leveler utilized to obtain a generally flat end.

As shown at FIG. 9B (e.g., as compared to FIG. 9A), the mask 821 (e.g.,photoresist, etc.) is stripped. The mask 821 may be removed in any of avariety of manners (e.g., chemical stripping, ashing, etc.). As shown atFIG. 9C (e.g., as compared to FIG. 9B), the UBM seed layer 813 (e.g., atleast the portion that is not covered by the interconnection structure832) is removed (e.g., chemically etched, etc.). Note that during theetching of the seed layer 813, a lateral edge portion of at least theseed layer 813 may, for example, be etched. Such etching may, forexample, result in an undercut beneath the interconnection structure 832and/or UBM 831.

In summary, various aspects of the present disclosure provide astructure and method for performing metal-to-metal bonding in anelectrical device. For example and without limitation, various aspectsof this disclosure provide a structure and method that utilize aninterlocking structure configured to enhance metal-to-metal bonding.While the foregoing has been described with reference to certain aspectsand examples, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the disclosure. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the disclosure without departing from its scope.Therefore, it is intended that the disclosure not be limited to theparticular example(s) disclosed, but that the disclosure will includeall examples falling within the scope of the appended claims.

1-20. (canceled)
 21. A semiconductor device comprising: a firstsubstrate comprising a first metal contact structure that comprises ametal, the first metal contact structure comprising a convex-shaped end;a second substrate comprising a second metal contact structure thatcomprises the metal, the second metal contact structure comprising aconcave-shaped end; and a metal-to-metal bond between the convex-shapedend and the concave-shaped end at a bonding region that is asymmetricabout a longitudinal axis of the concave-shaped end.
 22. Thesemiconductor device of claim 21, comprising a gap between theconvex-shaped end and the concave-shaped end at a peripheral edge of atleast one of the convex-shaped end and the concave-shaped end.
 23. Thesemiconductor device of claim 21, wherein the bonding region is shiftedtoward a first side of the concave-shaped end.
 24. The semiconductordevice of claim 23, wherein the bonding region is shifted toward thefirst side of the concave-shaped end by at least 5% of a width of thefirst metal contact structure.
 25. The semiconductor device of claim 21,wherein the bonding region is larger on a first side of theconcave-shaped end than on a second side of the concave-shaped end. 26.The semiconductor device of claim 25, wherein the bonding region is atleast 5% larger on the first side of the concave-shaped end than on thesecond side of the concave-shaped end.
 27. The semiconductor device ofclaim 21, wherein at least one of the first metal contact structure andthe second metal contact structure comprises a copper pillar.
 28. Thesemiconductor device of claim 21, wherein: the first metal contactstructure comprises first copper; the second metal contact structurecomprises second copper; and the metal-to-metal bond is a directcopper-to-copper bond.
 29. The semiconductor device of claim 21,wherein: the first metal contact structure comprises first copper; thesecond metal contact structure comprises second copper; and themetal-to-metal bond comprises at least one intervening metal between thefirst copper and the second copper.
 30. The semiconductor device ofclaim 21, wherein at least one of the first and second substratescomprises a semiconductor die.
 31. A semiconductor device comprising: afirst substrate comprising a first metal contact structure thatcomprises a metal, the first metal contact structure comprising aconvex-shaped end; a second substrate comprising a second metal contactstructure that comprises the metal, the second metal contact structurecomprising a concave-shaped end; a metal-to-metal bond between theconvex-shaped end and the concave-shaped end; and a gap between theconvex-shaped end and the concave-shaped end at a peripheral edge of atleast one of the convex-shaped end and the concave-shaped end.
 32. Thesemiconductor device of claim 31, wherein the gap is larger at a firstportion of the peripheral edge than at a second portion of theperipheral edge.
 33. The semiconductor device of claim 31, wherein afirst one of the first metal contact structure and the second metalcontact structure overhangs a second one of the first metal contactstructure and the second metal contact structure.
 34. The semiconductordevice of claim 31, wherein the gap extends completely around theperipheral edge.
 35. The semiconductor device of claim 31, wherein thegap is a largest gap between the convex-shaped end and theconcave-shaped end.
 36. A method of manufacturing a semiconductordevice, the method comprising: providing a first substrate comprising afirst metal contact structure that comprises a metal, the first metalcontact structure comprising a convex-shaped end; providing a secondsubstrate comprising a second metal contact structure that comprises themetal, the second metal contact structure comprising a concave-shapedend; and pressing the convex-shaped end and concave-shaped end togetherto form a metal-to-metal bond at a bonding region that is asymmetricabout a longitudinal axis of the concave-shaped end.
 37. The method ofclaim 36, wherein the bonding region is shifted toward a first side ofthe concave-shaped end.
 38. The method of claim 36, wherein the bondingregion is larger on a first side of the concave-shaped end than on asecond side of the concave-shaped end.
 39. The method of claim 36,wherein: the first metal contact structure comprises first copper; thesecond metal contact structure comprises second copper; and themetal-to-metal bond is a direct copper-to-copper bond.
 40. The method ofclaim 36, wherein: the first metal contact structure comprises firstcopper; the second metal contact structure comprises second copper; andthe metal-to-metal bond comprises at least one intervening metal betweenthe first copper and the second copper.